These research program projects are aimed at methodology development and the evaluation of Emergency Medical Services Systems interventions (Project 1), service interventions (Project 2), and Clinical interventions (Project 3). Project 1 will generate through clinical teams specifications of appropriate resource levels for hospital and ambulance emergency facilities. These categorization standards will be applied to the Baltimore regional EMS system to assess the impact of system interventions (categorization, ambulance and communications improvements) currently underway. Project 2 will assess the impact of such service interventions as triage nursing, patient exit interviews, patient advocacy, nursing audit, non-urgent walk-in clinics, and asthematic patient education groups. Project 3 will assess the impact of clinical interventions to be introduced at the Johns Hopkins Hospital and the Baltimore City Hospital emergency departments. Projects 2 and 3 will utilize random allocation of eligible patients to experimental and control groups while Project 2 will additionally develop methodologies to assess non-urgent use of emergency departments and indicated alternative treatment sites, the use of non-E.R. sites during illness episodes, and the attitudinal responses of patient groups to urgent and non-urgent hypothetical symptoms.